# Innovations in applied physics

## 32 GHz сold cathode magnetron with spaсe harmonics – nonlinear analytical calculation and 3d-simulation

The analytical estimation of the optimal parameters fulfilled for pulsed magnetrons with cold secondary-emission cathodes, operating at a frequency of 32 GHz with anode voltage of 8 kV and with magnetic field of about 0.4 Tesla. As shown, the geometry of the magnetron interaction space can ensure an interaction between electrons and the high-frequency field as for the (−1)-th space harmonic of π/2-oscillations, so for (+1)- th space harmonic π-oscillations in the drift-orbit resonance mode.

## Wideband chaotic generation and optimization of characteristics in microwave generator with electronic feedback and magnetic periodic focusing system

With the help of 2D numerical model it has been investigated the nonlinear dynamics and generation of wideband chaotic signals in the generator based on electron beam with the virtual cathode. It has been discovered the strong influence of the external non-uniform magnetic field on the nonlinear dynamics of the virtual cathode in the system. It has been analyzed the physical processes responsible for the discovered dependency of dynamics of the electron beam with the virtual cathode on the parameters of the external nonuniform magnetic field.

## Temperature effect on drift velocity of electrons in superlattice in electric and tilted magnetic fields

The work studies the effects of temperature on drift velocity of the electrons in semiconductor superlattices in electric and tilted magnetic fields. It is shown that a thermal distribution of the electrons can counter-intuitively enhance the phenomena related to resonances between the Bloch and the cyclotron frequencies of electron motion in superlattices. In particular, the increase of temperature leads to more prominent resonant maxima in the dependence of drift velocity of electrons on the strength of an electric field.

## Characteristics of the nonlinear left-handed waveguide

The modes of the planar dielectric waveguide made from nonlinear metamaterials with both negative permittivity and permeability are investigated. The dependencies of the propagation coefficients of the guided mode on the transmitted power are studied. The fields distributions are calculated for the systems with variable permittivity and permeability profiles. It is shown that in such systems a drastic increase in the field magnitudes may occur.

## Mathematical model and its numerical realization for the investigation and optimization of generators with electron feedback

It was stated in the paper the mathematical model and its numerical realization for the investigation of wideband chaotic oscillations and of physical processes in the electron beams with virtual cathode at the generators with electron feedback. Also it was briefly described the developed program package for the modeling of nonstationary nonlinear physical processes at the electron generators with virtual cathode and for calculating of output characteristics of devices.

## Higher harmonics generation in a relativistic electron beam with virtual cathode

The study of the microwave generation regimes with intense higher harmonics taking place in a high-power vircator consisting of a relativistic electron beam with a virtual cathode has been made. The characteristics of these regimes, in particular, the typical spectra and their variations with the change of the system parameters (beam current, the induction of external magnetic field) as well as physical processes occurring in the system have been analyzed by means of 3D electromagnetic simulation.

## Submillimeter-wave magnetron with the elongated anode: optimal parameters of oscillatory circuit

The estimation of optimal parameters with the analytical model regarding nonlinear electron motion dynamics is fulfilled for the submillimeter-wave M-type oscillator tor operating on frequency about 0.33 THz with anode voltage 13 кV and magnetic field 0.7 Т. Revealing from this model, the magnetron interaction space geometry providing the effective electron interaction with a high-frequency field on (+1) spatial harmonic of π-mode oscillations is proposed for the drift-orbital resonance regime.

## The electrodynamic characteristics of multirow interdigital slow wave structure

The results of an experimental study the dispersion characteristics and field distribution of main and higher order modes of multirow interdigital slow wave structures with their resized are presented. The ways of increasing the frequency separation of main and higher order modes and the working excitation band of the main mode are offered. Investigation the forced oscillations of the multirow interdigital slow wave structure with exponential H-waveguide power ports has shown the possibility of a single-mode excitation in a wide bandwidth.

## Modeling of radio-frequency identification tags antennas

The method of combined volume and surface integral equations has been proposed for simulation of radio-frequency identification tags. Their approximate models have been built to calculate the input impedance and the radiation pattern. Various planar and nonplanar tag’s structures have been considered and their parameters have been obtained.

## Nonlinear dynamics of long mirrorless fiber raman laser

Numerical model of long fiber Raman laser is proposed. The model based on the equations, describing the propagation of pump and Stokes waves, linear coupling of oppositely running waves due to scattering and its nonlinear interaction. The derivation of equations for slowly varying pulse envelopes uses the field decomposition in terms of spatial harmonics rather then commonly used temporal harmonics, which allows to avoid the twopoint boundary conditions, and to employ the numerical scheme of Courant–Isaakson–Rees.